|Warning: If you have used S/MIME for email encryption, you should export certificates in order to retain a backup copy, before deleting them from the browser.|
[How can I tell if I've used S/MIME for email encryption?].
- Navigate, in Finder, to Applications > Utilities > Keychain Access.
Double-click to open Keychain Access.
- Select the login keychain, and then select My Certificates from the list in the lower pane.
If you do not have a list in the lower pane, with All Items, Certificates, Passwords..., press the button in the bottom left of the Keychain Access window. Your window should look like the image below:
- Highlight all certificates.
- Follow the menu path Edit > Delete, or press the delete key on your keyboard.
Result: A popup windows prompts to confirm deletion of the certificate. Click Delete.
- Select "All Items" from the Category list in the lower left-hand page. Click "Kind" to sort the certificate items by their type
- Select everything that has the type "identity preference" and Delete them.
- Type "MIT Certification" into the search box in the upper right hand corner.
- Highlight the MIT Certification Authority certificate and Delete it.